The relentless rush of water turned whole towns into muddy swamps and brought most transportation to a standstill. Damage assessments were on hold as authorities tried to rescue more than 2,500 people stranded in an emergency that stretched from Colorado Springs all the way to the Wyoming border.

A break in the weather aided crews as they ferried a dozen residents at a time out of Lyons and other mountain towns that had been cut off by high water. The Colorado National Guard tweeted that it helped evacuate nearly 300 people from Lyons and on Friday added helicopter flights to the search-and-rescue efforts, spokeswoman Cheresa Theiral said.

Many roads remained impassable, and still more rain was expected later in the day.

The overflowing St. Vrain River sliced the town of Longmont in half. All major roads were closed, and several thousand homes and businesses were without power.

“This one’s going to bring us to our knees,” said Tom Simmons, president and co-owner of Crating Technologies, a packing service that had its warehouse inundated. “It’s hoping against hope. We’re out of business for a long time.”

Most of those who were stranded were not in immediate danger. And many chose to stay behind with loved ones or to watch over their property. But at least three people have been killed and another person was missing.

The rains forced hundreds of people to seek emergency shelter up and down Colorado’s heavily populated Front Range, which has received more than 15 inches of rain this week, according to the National Weather Service.

That’s about half the amount of precipitation that normally falls in the foothills near Boulder during an entire year.

Boulder County officials said 20 people were unaccounted for Friday. But, he noted, that doesn’t necessarily mean they are missing.

“It means we haven’t heard back from them,” county spokesman James Burrus said.

Wherever the muddy water gushed, it created an astounding mess and countless inconveniences. In at least one community, the flooding caused sewer grates to erupt into huge black geysers.

The National Park Service closed Rocky Mountain National Park and was escorting people from nearby Estes Park along a trail over the Continental Divide.

About 90 miles of Interstate 25 were closed Friday from Denver to Cheyenne, Wyo., because of flooding on the St. Vrain, Poudre and Big Thompson rivers, transportation officials said.

Two backpackers got stranded by an ice storm that resulted from the same weather system that caused the flooding.

Suzanne Turell and Connie Yang of York, Maine, last sent a text message Thursday with their GPS coordinates, but their cellphones went dead. The pair hiked off Longs Peak just as the National Park Service was organizing a rescue effort.

Boulder officials told about 4,000 people living along Boulder Creek to head for higher ground as debris and mud coming off the mountainsides caused the creek to rise rapidly Thursday night, authorities said.

The creek’s waters ran a cafe-au-lait color and began to recede after midnight, but conditions remained dangerous, authorities said.

The entire hamlet of Eldorado Springs, home to about 500 people, was also urged to evacuate because of a flash flood and mudslide threat along South Boulder Creek, Burrus said.

In Fort Collins, neighborhoods along the Cache La Poudre River were evacuated overnight, with the river expected to rise to nearly 2 feet above flood stage Friday, according to the weather service.

The city closed bridges after water began topping Seaman Reservoir in the Poudre Canyon. Residents were warned to stay clear of the river.

In Lyons, residents took shelter on higher ground, including some at an elementary school, before National Guard convoys pushed through the water.

Dawn Lundell and John Johnson decided not to wait, instead hiking from the town through 200 yards of water in a canal. They described a “calm, reasonably festive” atmosphere among those who remained.

“Nobody minds roughing it a little bit in Lyons. We’re all outdoorsy people. We call it Mayberry. Everybody helps each other,” Lundell said.

By Friday afternoon, National Guard helicopters had rescued almost 300 people who got stuck in the small community of Jamestown, northwest of Boulder. County spokeswoman Liz Donaghey said two choppers were airlifting as many people as they could carry.

The weather service warned Friday of more flash flooding in Loveland. In the town of Drake, the Big Thompson River was more than 4 feet above flood stage. The Big Thompson caused the deadliest flash flood in state history in 1976, when about a foot of rain fell in just four hours, killing 144 people.

Jose Ayala spent Friday morning picking through what was left of his family’s possessions in their two-story farmhouse near Berthoud. He and his sons watched the waters rise all Thursday evening, finally making the decision to flee at 11 p.m. with some documents and a computer.

“The rest is in the house. All gone, basically,” Ayala said.

Some of the flooding was exacerbated by wildfire “burn scars” that have spawned flash floods all summer in the mountains. The flames strip away vegetation that normally helps absorbs excess water and leave a residue behind that sheds water.

One person was killed when a structure in Jamestown collapsed. Another man drowned in floodwaters north of Boulder while trying to help a woman who was swept away after a vehicle got stuck in water. She was missing. To the south, Colorado Springs officers found a man’s body in Fountain Creek.

Rain from the same storm also drenched drought-stricken New Mexico, sending rivers out of their banks, closing roads and stranding children at schools. Evacuations were reported from Las Vegas to Truth or Consequences.